Field of the Invention
The invention relates, in general, to a method for route searching from a terminal of a calling subscriber, that is connected to a first communications network, to a terminal of a called subscriber that is connected to a second communications network. The method is used in the situation where call diversion to a diversion destination is activated for the terminal of the called subscriber. For setting up the call, the address of the terminal of the called subscriber is initiated by the terminal of the calling subscriber. In particular, the invention relates to a method for route searching when the terminal of the calling subscriber and the diversion destination are not in the communications network to which the terminal of the called subscriber is assigned.
For example, the "HICOM 600 System" product document from Siemens AG, Order Number A19100-K3161-G430-01 describes a communications system which provides the service features of call diversion and automatic call forwarding (pages 29 and 38). The service feature of call diversion means that a call to a terminal whose call line is activated is diverted to a selected destination terminal. The "HICOM 300 Networking" product document from Siemens AG, Order Number A31001-W-A30, also describes the interconnecting communications systems to form a network and providing locally available service features throughout the network, so that call diversion is possible to a terminal assigned to this network.
If a subscriber network including such communications systems is connected to a public communications network, calls may be diverted from a terminal that is connected to the subscriber network to terminals that are connected to this specific subscriber network and also to terminals that are connected to the public communications network. If the terminal of a calling subscriber is connected to the public communications network and the terminal of a called subscriber, for which call diversion to a diversion destination is activated, is connected to the subscriber network, then a route searching procedure can be carried out to determine the route to the diversion destination in the subscriber network or in the public communications network. If the route searching procedure is carried out in the public communications network, then the address of the diversion destination is transmitted back to the network node to which the terminal of the calling subscriber is assigned. Starting from this network node, a new connection is set up to the network node to which the diversion destination is assigned.
Depending on the network association of the terminals of the calling subscriber, of the called subscriber, and of the diversion destination, an operator of a subscriber network incurs a different cost when the route searching procedure is carried out in the external communications network than when the route searching procedure is carried out in its own communications network.
If the terminal of the calling subscriber and the diversion destination are assigned to the public communications network and the terminal of the called subscriber is assigned to the subscriber network, and if the diversion destination can be reached from the subscriber network via the same network gateway via which the incoming call is made, then two connections of the network gateway group from the public communications network to the subscriber network are used for initializing the route searching procedure in one's own subscriber network. If, for example, the terminal of the calling subscriber and the diversion destination are assigned to a communications network in Hamburg, and if the terminal of the called subscriber is connected to a subscriber network in Munich, then, when the route searching procedure is carried out in the subscriber network in Munich, two trunk connections are used from Hamburg to Munich, and vice versa, even though only one local connection would be required in Hamburg. The subscriber network operator thus incurs costs for the connection from Munich to Hamburg via the public communications network. If, on the other hand, the diversion destination is assigned to one's own subscriber network, and if the route searching procedure is carried out in the external communications network, then the subscriber network operator incurs higher costs than if the route searching procedure were carried out in his own subscriber network.
In order to avoid the last problem described above, a comparison of subscriber call number sequences for the diversion destination with corresponding subscriber call number sequences in the subscriber network can be carried out in one's own subscriber network. If the two sequences match, then the diversion destination is in one's own subscriber network, and a route searching procedure can be carried out in one's own subscriber network. If the call number information items differ from one another, then the route searching procedure should be carried out in the external communications network.
"In zwei Schritten zum `Corporate Network`" [In two steps to the "Corporate Network"], telecom report 19 Issue 3, 1996, Siemens AG Berlin and Munich describes a private communications network. This private communications network (ISDN network) comprises a plurality of network nodes, which each have a unique node identity (for example node 3 Burda media). The communications network is connected to the public communications network via various S2M exchange accesses in different towns. In addition, the private communications network has a direct link to a GSM mobile radio network (D1, D2) via a GSM output.